Atoms, very small particles, are made of even smaller particles (a particle is just a small amount of matter that stay "clumped" together, and that can be characterized by mass, volume, density, and so on).

Every atom has electrons, which are particles that have negative electrical charges; every atom also has protons, which are particles that have positive electrical charges.

In terms of mass (how much "stuff" there is in an object), a proton has approximately 1800 times the mass of an electron, but its electrical charge is exactly equal to the charge of the electron, just positive instead of negative.

With the exception of some hydrogen atoms, every atom also has neutrons, which are particles with the same mass as protons but no charge, positive or negative. Many atoms have the same number of neutrons and protons, and electrically neutral (no total positive or negative charges) atoms all have the same number of electrons as protons. For example, an electrically neutral hydrogen atom has one proton and one electron; an electrically neutral helium atom has two protons, two neutrons, and two electrons.

Protons and neutrons are made of even smaller particles called quarks. All these particles interact with one another and are held together by different forces. Part of the mystery of particle physics is that an atom has a radius about 100,000 times the radius of a proton, which means that atoms are actually mostly empty space! Yet atoms are one of the fundamental particles that make things what they are - the properties of different atoms make salt different from baking soda and different from water. It is this mystery of physics that drives some physicists to study the nature of these particles.